Design of off-grid solar lighting system based on LED

Solar photovoltaic power generation can directly convert solar energy into electrical energy. It is a new technology for obtaining electricity in a clean and low-carbon way. It is also a very important and promising technology among the many ways to utilize solar energy. People have tried to apply solar power generation technology to lighting for a long time. In recent years, with the rapid development of LED technology and the continuous decline in the price of solar modules, LED-based solar lighting has been used more and more. Among them, off-grid lighting systems are increasingly attracting people's attention due to their maintenance-free, no need to lay cables, and low operating costs. 1. LED-based off-grid solar lighting systems are widely used Today, among the nearly 7 billion people, about 4 billion are classified as the bottom of the "income pyramid" due to their relatively low economic income. Their power facilities are incomplete, and their lighting is mainly based on fuel. Among them, about 1.6 billion people have no power facilities at all, and their lighting depends on fuel lighting, such as kerosene lamps and candle lamps. According to statistics, fuel lighting consumes about 77 billion liters of fuel each year, and the corresponding cost is about 38 billion US dollars. Light sources such as candles and kerosene lamps are not only low in brightness, easy to catch fire, poor in portability, and smoky, but also have high operating costs. LED-based off-grid solar lighting systems are an ideal solution for this market due to their safety, portability, maintenance-free and operating cost-free features. In the construction of new rural areas, many rural public roads can adopt this lighting system. Since it does not require laying cables, is a one-time investment, maintenance-free and operating cost-free, this system has been promoted in many rural construction projects in China, such as the "Thousand Villages Plan" promoted by the Climate Organization and the One Foundation. Compared with before use, these systems have greatly facilitated the evening outdoor activities of residents in these villages. Others such as garden lights can also be seen in off-grid lighting systems. In addition, off-grid lighting has also become an alternative for some professional road lighting. 2. Introduction to off-grid solar lighting systems Below we briefly introduce the off-grid solar lighting system. A typical off-grid solar lighting system can be represented by Figure 1.











As shown in the figure, a typical off-grid lighting system can be divided into the following parts from the functional point of view.

Solar panels: Solar panels are the energy converter of the whole system, which can convert sunlight into electrical energy. According to different materials, solar panels include monocrystalline silicon, polycrystalline silicon, amorphous silicon, GaAs, CIGS, etc. Due to price, technology and other reasons, more than 90% of applications use monocrystalline silicon or polycrystalline silicon solar panels.

Charge and discharge controller: On the one hand, this controller will store the electricity generated by solar panels in the energy storage unit in the system, such as rechargeable batteries. On the other hand, this controller will also control the battery that stores electrical energy to controllably provide electrical energy to the load in the system, that is, the lighting system. Battery charge and discharge protection is a necessary function. In order to convert the sunlight collected by solar panels into electrical energy and store it in the battery to the greatest extent, some controllers have maximum power tracking function. A good charge and discharge controller can save solar panels to a certain extent and extend the service life of rechargeable batteries.

Rechargeable batteries: It stores the electrical energy generated by solar panels and provides energy supply for lighting systems. Lead-acid batteries, nickel-hydrogen batteries, and even lithium iron phosphate batteries can be used. Considering the cost and stability, lead-acid batteries and nickel-metal hydride batteries are the main choices.

Lighting system: It usually includes light sources, such as LED or LED array, light source driver, lamps, etc. Some lighting systems also include environmental parameter detection devices, human-computer interaction interfaces, etc.

III. Design of off-grid solar lighting system

1. Design criteria

Since the off-grid solar lighting system is a completely independent system and solar energy is its only energy source, it must be designed based on the "worst" working conditions. For the selected area or location, the worst working conditions mainly refer to the "worst" season, that is, the "winter" months, such as December and January in the northern hemisphere and June and July in the southern hemisphere. The reasons are:

(1) The night is the longest, that is, the lighting time is the longest (if the whole night is required to be lit), and the corresponding energy consumption is the largest;

(2) The day is the shortest, that is, the solar radiation time is the shortest, and the solar radiation intensity is also small, so the corresponding radiation energy is the smallest, and the power generation of the solar module is the least;

(3) Winter is the coldest, and the usable capacity of the battery is also the smallest.